In manual or hand held electrostatic paint spray guns, a manually operated trigger moves a valve needle in a linear direction to open a paint valve for initiating spraying. In one common type of spray gun, an electrode projects from the end of the valve needle through a paint discharge orifice. The electrode is connected to a high voltage power supply for imparting an electrostatic charge to the paint as it is atomized. The electrode may be, for example, maintained at from 20,000 to 80,000 volts dc, or more, relative to the grounded workpiece which is being painted. In an automatic spray gun used for larger scale production, the manual trigger is replaced with an automatic trigger mechanism which reciprocates the valve needle in a linear direction in response to, for example, an electric signal or a pneumatic signal.
In either type of electrostatic spray gun, it is necessary to maintain a continuous electrical connection between the power source and the paint charging electrode as the electrode and the supporting valve needle are reciprocated by the trigger mechanism. In U.S. Pat. No. 4,335,851 to Hastings, a spray gun is shown in which a pin extends perpendicularly through and projects from opposite sides of an electrically insulated valve needle. The paint charging electrode which projects from the front of the valve needle is electrically connected to the pin. A wire is embedded in the electrically non-conducting spray gun barrel to connect a high voltage source to a step in a bore through the barrel in which the valve needle is reciprocated. A spring is compressed between the end of the wire at the step and the pin through the valve needle to establish electrical contact between the wire and the electrode as the valve needle is reciprocated. In U.S. Pat. No. 4,721,255 to Lind, the paint charging electrode projects from the front of the valve needle and also projects from the side of the valve needle and extends along the side of the valve needle parallel to the axis of the valve needle. The portion extending parallel to the side of the valve needle presses against a fixed contact mounted in the gun barrel. The fixed contact is connected to the high voltage power source to maintain an electrical connection as the valve needle is reciprocated.